The invention relates to a lens system for monochromatic, or almost monochromatic light, in which the focal distance can be adjusted for parallel, or substantially parallel, incident light to be refracted together to one focal point, which coincidences with, for example, the end surface of an optical fibre. Then the lens system can be applied in for example coupling arrangements, for axially connecting the end sections of at least one optical fibre to each other, which are fixed in at least one plug each being arranged in one coupling house, for achieving an optical connection between the fibres, or wherein parallel or substantially parallel, light of one or several adjacent monochromatic light sources to be coupled into one optical fibre with maintained good performance.
The fast development of the communication area has increased the demand for faster and more reliable transmission medias drastically. The optical fibres have revolutionized the transmission possibilities. These fibres allow a large number of signals to be transferred in one and the same fibre with the speed of light. As a consequence of the fibre length being limited when manufactured, these must be coupled together by means of different coupling arrangements.
The coupling arrangements must couple together fibres with each other so that the fibre ends are located exactly in front of each other. A problem at the connection of the optical fibres is the insignificant diameter of the fibres, being some or some tenth of a millimetre, while the core of the fibres may have a diameter of 10to 50 xcexcm. Thus, a radial deviation of some thousandth of a millimetre in the connection causes a large deviation, whereby the transmission losses drastically increase. Hence, very large requirements are put on the tolerances of the coupling device, causing complicated constructions and high manufacturing costs.
In a large number of patent applications, a number of coupling arrangements for optical fibres are known. These arrangements demand specially shaped means for centring the optical fibres relative to each other.
An example of the previously known coupling arrangement is the U.K. patent GB 2002136, in which a spherical lens is used for transmission of light signals, and U.S. 4,451,115 in which the lens devices are radially adjusted in one coupling device each, for compensating for defects built-in with the purpose to optimise the transmission of the light between two fibre ends. In none of the known cases a lens device is described, which can be used for coupling in parallel, or substantially parallel, light into an optical fibre, neither for transmission of light signxcx9cbetween two optical fibres with maintained optimum transmission of the light signal in more than one wavelengths.
The object of the present invention is to provide a coupling device for very thin fibres, enabling a very safe and accurate centring and coupling of the fibre ends, enabling to couple fibres of different sizes together, which counteracts deformation of the optical fibres at the connection, which is adjustable for the transmission wavelength being used, minimizing the reflexes in the optical end surfaces of the optical fibres, and admitting more than one fibre channel to be transferred through one and the same lens system. Furthermore, manufacturing of the coupling device will be simple and cheap.
The objects have been solved by each lens system being constituted partly of a lens body, the front end surface of which is convex, for instance spherical, partially spherical or aspherical, and the rear opposite end surface of which is arranged perpendicular to the longitudinal axis of the lens body, partly of a space with a plastic, optical medium, for instance air, an oil or a refractive index adapted gel, partly of a rear glass body, the function of which is to achieve a rear limitation for the optical means, partly to guarantee a good optical contact with the optical fibre, which is mounted in physical contact with the glass body. The front end surface of the glass body, facing the plastic medium, may be convex or plane, while the rear end surface is preferably plane.
The lens body is characterised in that its rear focal point, for the wavelength used in the fibre optical application, is placed outside its rear end surface.
The lens system is characterised in that it contains three optical elements, the middle of which is plastic, that the rear glass body can be displaced in the axial direction by means of the pressure being achieved by the end surface of the optical fibre contact at the mounting of the contact in the coupling arrangement, and consequently that the rear focal point for the lens system always can be brought to coincidence with the rear end surface of the rear glass body.
The end surface of the fibre contact can be plane surface grinded or spherically grinded. In both cases, a very good optical contact between the end surface of the optical fibre and the rear end surface of the glass body is obtained, due to the elastic connection of the rear glass body.